The precise metering of dry solids such as amorphous powders is an important, and often a difficult task in many applications. Whenever such materials are continuously fed into a process, the feed rate at which the material is delivered to the process must be controlled to ensure accuracy.
One type of dry solids feeding system is a volumetric feeder. As the name implies, volumetric feeders dispense material by volume. They employ a displacement measuring mechanism of some sort (for example, an auger mounted below a supply vessel and feeding a fixed volume of material per auger rotation) operating at a set speed. This results in feeding a known volume of material. The weight of material fed can generally be determined based on the material's bulk density. Other dry solids feeding systems are designed to weigh the product, where the weight measurement can be used to control the material feed rate. Such so-called "gravimetric" systems include loss-in-weight, weigh belt and weigh auger feeding systems.
Some materials, however, have a tendency to clump together or stick to the side of the supply vessel. Further, certain materials have a tendency to resist flow out of its supply vessel (hopper) and "rat hole" or bridge. This will cause the material to be fed at a nonuniform rate, or totally stop feeding, adversely affecting the process. To overcome these problems, the supply vessel can be vibrated. This vibration causes the material to flow more uniformly out of the supply vessel (or hopper).
There are various well-known arrangements of dry solids feeders in which its supply vessel (or hopper) is vibrated to cause product to flow out from within. The most common of these arrangements, where the supply vessel is rigidly attached to the feeding mechanism, is to simply attach a vibrator directly onto one of the sides of the supply vessel to induce product flow out from within.
However, there are several drawbacks to this configuration. Firstly, vibratory forces become non-uniform in nature because the supply vessel cannot vibrate as a separate entity. Since the supply vessel is rigidly attached to, or an integral part of, the feeding mechanism, vibration is transmitted to the feeding mechanism as well. In effect, the entire feeding system vibrates (that is, both the supply vessel and the feeding mechanism). However, vibration is primarily concentrated in that area of the supply vessel where the vibrator is physically mounted, which does not allow uniform vibratory forces to reach the product within because the supply vessel itself does not vibrate uniformly. Consequently, the effectiveness of the vibrator to promote flow is reduced. Secondly, such designs do not lend themselves to longevity because the specific wall of the supply vessel, where the vibrator device is physically attached, frequently fatigues due to non-uniform forces produced by the vibrator on the rigidly attached supply vessel.
In another known configuration, the supply vessel (or hopper) straddles the feeding mechanism and is independently mounted on vibration isolators, with the isolators affixed to a separate structure. Such designs typically involve placing the supply vessel on three or four vibration isolators (usually rubber or spring type mountings), so that the vessel becomes completely resilient (i.e., it can vibrate freely).
In such arrangements, the supply vessel is usually conical in shape, but always includes a converging bottom with its outlet flexibly connected to a mating inlet on the feeding mechanism (feeder). To promote flow, a vibrator is attached to the side of the supply vessel which, when energized, causes the vessel to vibrate uniformly as a separate entity. Vibration is confined strictly to the vessel and not transmitted to the feeding mechanism.
Although such designs are usually very effective in promoting flow of dry solids from within a supply vessel, they are also quite costly to manufacture. In addition, such systems consume considerable space due to the additional structural framework that is necessary to support the independent assembly. Usually, the dimensional requirements of such a structure are much larger than the footprint of the actual feeding device to which it attaches.
Consequently, it is an object of the present invention to provide an apparatus which permits the resilient mounting of a supply vessel to the feeding mechanism such that the vessel can be vibrated to promote flow of product from within, the vessel will vibrate uniformly, and vibration of the supply vessel will not transmit to the feeding mechanism (i.e., a "live" independent hopper).
It is another object of the present invention to provide a feeding mechanism in which its supply vessel is isolated from the feeding mechanism without any additional structural requirement.
It is still another object of the present invention to provide a method for isolating the vibration of the supply vessel while directing the flow of material from the supply vessel to the feeding mechanism.
It is still another object of the present invention to provide a feeding mechanism in which material is fed from its supply vessel to the feeding mechanism without the escape of material.
It is a further object of the present invention to provide a method for mounting a supply vessel to a feeding mechanism such that the vibration of the supply vessel does not transmit to the feeding mechanism.
These and other objects of the present invention will become clear to one skilled in the art from the following description of the invention.